Gyro compass

ABSTRACT

A gyro compass having a gyro case housing therein a gyro and supported with freedom of three axes, functions for outputting a signal corresponding to an inclined angle of the gyro spin axis relative to the horizontal plane and a function for applying a torque around a vertical axis of the gyro case in proportion to an input signal, and a controller supplied with the signal corresponding to the inclined angle and a latitude value at which the gyro compass is located, wherein a constant relative to the input latitude value is set by the controller after the gyro compass is energized, a signal, which results from differentiating the signal corresponding to the inclined angle during a predetermined time, is added to a signal, which results from multiplying the signal corresponding to the inclined angle with the constant and an added result is set as the input signal, whereby a constant optimum north-seeking movement is carried out regardless of the change of the latitude value to thereby reduce a settle time. Also, the gyro compass having an error corrector supplied with the signal corresponding to the inclined angle, a speed signal of a navigation vehicle and its heading azimuth signal, wherein a bias error caused by the inclined angle of the gyro compass spin axis and an azimuth error caused by the movement of the navigation vehicle are estimated and calculated to thereby reduce an azimuth error caused by the bias error.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to marine gyro compasses and,more particularly, is directed to a fast settle apparatus and an errorcorrecting apparatus thereof.

2. Description of the Prior Art

Referring to the drawings in detail, and initially to FIG. 1, let usdescribe a gyro compass described in Japanese Patent No. 428317 as anexample of a conventional gyro compass to which a fast settle apparatusof the present invention can be applied.

The entirety of the gyro compass is depicted by reference symbol A inFIG. 1, and the gyro compass A includes a gyro case 1. As shown in FIG.1, the gyro case 1 houses therein a gyro rotor (not shown) which isrotated at high speed and at a constant revolution rate by an inductionmotor (not shown), and a rotary vector of the gyro rotor is directed tothe south (i.e., directed in the clockwise direction as viewing from thenorth). The gyro case 1 has a pair of vertical shafts 2, 2' protrudedfrom the upper and lower portions thereof, and these protruded verticalshafts 2, 2' are respectively fitted into inner rings of ball bearings4, 4' mounted to corresponding positions of a vertical ring 3 providedoutside of the gyro case 1. A suspension wire 5 is secured at its lowerend to the upper vertical shaft 2 and the upper end thereof is attachedto the vertical ring 3 by means of a suspension wire mount 5'.

According to the above-mentioned arrangement, the weight of the gyrocase 1 is not applied to the ball bearings 4, 4' of the vertical shafts2, 2' as a thrust load but is fully received by the suspension wire 5,thereby friction torque of the abovementioned ball bearings 4, 4' beingreduced considerably. A pair of liquid ballistics 6 are mounted on theeast and west of the vertical ring 3 in order to apply a north-seekingtorque to the gyro.

As shown in FIG. 2, each of the liquid ballistics 6 is a kind of acommunicated tube and is composed of reservoirs 6-1, 6-1' disposed inthe north and south of the gyro, liquid 6-2 of high specific gravitysubstantially filled into these reservoirs 6-1, 6-1' substantially up tothe halves thereof, an air tube 6-3 communicating the north and southreservoirs 6-1, 6-1' above and a liquid tube 6-4 communicating the northand south reservoirs 6-1, 6-1' below.

Referring to FIG. 1, it will be seen that a damping weight 7 is mountedon the west side of the gyro case 1 in order to damp the north-seekingmovement. As shown in FIG. 1, a primary coil 8-1 of a differentialtransformer for detecting a declination between the gyro case 1 and thevertical shafts 2, 2' of the vertical ring 3 is attached to the eastside of the gyro case 1, and a secondary coil 8-2 of the differentialtransformer is attached to the opposed position of the vertical ring 3,thereby constituting a follow-up pickup 8. The vertical ring 3 includesa pair of horizontal shafts 9, 9' protruded outwardly from the east andwest positions perpendicular to both of the vertical shafts 2, 2' and agyro spin axis. These horizontal shafts 9, 9' are respectively fittedinto inner rings of ball bearings 11, 11' attached to the correspondingpositions of a horizontal ring 10 provided outside of the vertical ring3. The horizontal ring 10 has a pair of gimbal shafts 12, 12' disposedat its positions within the horizontal plane and which are perpendicularto the horizontal shafts 9, 9'. These gimbal shafts 12, 12' arerespectively fitted into a pair of gimbal shaft ball bearings 14, 14'attached to a follow-up ring 13 disposed outside of the horizontal ring10.

As shown in FIG. 1, the follow-up ring 13 has upper and lower follow-upshafts 15, 15' and these follow-up shafts 15, 15' are respectivelyfitted into follow-up shaft ball bearings 17, 17' disposed at theopposing positions of a binnacle 16.

The upper follow-up shaft 15 has a compass card 18 attached at its shaftend and an azimuthal angle in the bow is read by the cooperation of thecompass card 18 and a lubber line 18B secured to the binnacle 16 at thecorresponding position in the bow side. An azimuth servo motor 19 isattached to the lower portion of the binnacle 16, the rotary shaft 19Aof which is coupled through an azimuth pinion 20 to an azimuth gear 21located at the lower portion of the follow-up ring 13. An azimuthtransmitter 22 is attached to the lower portion of the binnacle 16 andits rotary shaft 22A is meshed with the azimuth gear 21 via a gearsystem (not shown), whereby an azimuth signal is converted into anelectrical signal by the azimuth transmitter 22, which is transmitted tothe outside.

The part within the horizontal ring 10, that is, the part including thehorizontal ring 10, the vertical ring 3, the gyro case 1 or the like isnormally called a gyro sensitive unit. The gyro sensitive unitconstructs a vertical physical pendulum around the gimbal shafts 12,12', whereby the horizontal shafts 9, 9' are constantly kept within thehorizontal plane regardless of ship's inclination.

If there is a difference between the azimuth of the gyro case 1 and theazimuth of the vertical ring 3, then such difference is detected andconverted into an electrical signal by the follow-up pickup 8 providedbetween the gyro case 1 and the vertical ring 3. The resultantelectrical signal is amplified by an external servo amplifier 23 andsupplied to the azimuth servo motor 19 (which forms an azimuth servosystem). The rotation of the azimuth servo motor 19 is transmittedthrough the rotary shaft 19A, the gear train (not shown) and the azimuthgear 21 to the follow-up ring 13 and is further transmitted through thehorizontal ring 10, the horizontal shafts 9, 9' or the like to thevertical ring 3, thereby constantly holding the azimuthal error betweenthe vertical ring 3 and the gyro case 1 at zero.

Owing to the action of the azimuth servo system, the horizontal shafts9, 9' and the gyro spin axis are constantly kept in an orthogonalrelation and the gyro can be prevented from being applied with twistingtorque. That is, owing to the actions of the three shafts such as thevertical shafts 2, 2', the horizontal shafts 9, 9' and the gimbal shafts12, 12, having the servo system, the gyro case 1 is completely isolatedfrom the angular motion of the ship, thereby the gyroscope beingconstructed.

The above-mentioned liquid ballistics 6 are adapted to give thegyroscope the north-seeking force, i.e., function as the compass.

The principle of the liquid ballistic 6 will be described with referenceto FIG. 2. FIG. 2 shows the case such that the north-seeking end of thegyro is inclined from the horizontal plane by an angle θ. In this case,assuming that the ship is in its stopped condition, then the liquidsurface of the liquid 6-2 becomes perpendicular to the direction ofgravity force g. Therefore, as compared with the case such that theinclination of the north-seeking end relative to the horizontal plane iszero, the liquid at the hatched portion of FIG. 2 is decreased in thenorth-side reservoir 6-1' and is increased in the south-side reservoir6-1. Assuming now that r₁ is a distance from the horizontal shafts 9, 9'to the center of the two reservoirs 6-1, 6-1', S is a cross section areaof the two reservoirs 6-1, 6-1' and ρ is a specific gravity of theliquid 6-2, then the weight of the liquid at the inclined portion isexpressed as:

    S×r.sub.1, sin×ρ×g

Since the above-mentioned weight unbalance occurs in the two south andnorth reservoirs 6-1, 6-1' and the moment arm from the horizontal shafts9, 9' is r₁, a torque T_(H) produced about the horizontal shafts 9, 9'by the liquid ballistics 6 when the north-seeking end of the gyro isinclined from the horizontal plane by θ is approximately calculated as:

    T.sub.H =2 S r.sub.1.sup.2 g ρθ

    2Sr.sub.1.sup.2 gρ=K

where K is the ballistic constant. That is, the liquid ballistics 6 actto apply the torque proportional to the inclination relative to thehorizontal plane of the gyro spin axis to the surrounding of thehorizontal shafts 9, 9, of the gyro, thereby rendering the north-seekingforce to the gyro. Thus, the gyro is rendered the gyro compass.

As described above, we have considered so far the case that the ship isin the still condition. In this case, assuming that α_(N) is asouth-north component of ship's acceleration due to increase anddecrease of ship's speed, ship's turning or the like, a torque T_(H1)generated from the liquid ballistic 6 under the ship's sailing conditionis expressed by the following equation: ##EQU1## As shown in FIG. 3, thedamping weight 7 is attached to the gyro case 1 with a distance r₂ (inthe direction perpendicular to the sheet of drawing) from the verticalshafts 2, 2' within the plane including the vertical shafts 2, 2' andperpendicular to the gyro spin axis. FIG. 3 shows the gyro case 1 underthe condition such that the north-seeking side of the gyro is inclinedupward from the horizontal plane by the angle θ as viewing from thewest. As shown in FIG. 3, a gravitational acceleration g acts on thedamping weight 7 of mass m so that a force of m×g acts on the dampingweight 7 in the vertical direction. In this case, let us consider thatthis force is divided into a component m g cos θ parallel to thevertical shafts 2, 2' and a component m g sin θ the vertical shafts 2,2' acts only as a load on the vertical shaft ball bearings 4, 4', whilethe component m g sin θ parallel to the spin axis acts on the gyro as atorque multiplied with a distance r₂ from the vertical shafts 2, 2'around the vertical shafts 2, 2'. Assuming that Tφ represents the abovetorque, then the torque Tφ is approximately given by the followingequation:

    Tφ=μ·θ

where μ=m g r₂.

That is, the damping weight 7 can be regarded as the apparatus whichapplies the vertical axes 2, 2' of the gyro with the torque proportionalto the inclination of the gyro spin axis relative to the horizontalplane, and the north-seeking motion of the compass can be damped by thedamping weight 7.

Further, a torque Tφl generated during the ship's sailing is expressedby the following equation, considering the acceleration caused by ship'smotion: ##EQU2##

FIG. 4 shows in block form a principle of the conventional gyro compassof FIG. 1, that is, the north-seeking motion of the conventional gyrocompass in which an azimuthal error φ and an inclined angle θ from thedue north of the north-seeking end of the gyro spin axis are assumed tobe variables and which copes with their initial errors φ.sub. , φ.sub.are expressed by Laplace operator and transfer function in a block form.In FIG. 4, ω represents earth rotation angular velocity, H angularmomentum of gyro, λ latitude of that spot, K north-seeking constant(ballistic constant), μ damping constant and S Laplace operator.

If now there is the azimuthal error φ, then a component in which theazimuthal error φ is multiplied with a horizontal component ω cos λ100of the earth rotation velocity ω acts on an element 101 around thehorizontal axis of the gyro as an angular velocity input, therebygenerating the gyro angle θ together with an initial inclined angleθ.sub. . The vertical ring 3 is similarly inclined by the inclinationangle θ of the gyro spin axis, and the liquid ballistic 6 attached tothe vertical ring 3 is also inclined, thereby the liquid 6-2 within theliquid ballistic 6 being moved in the lower reservoir, thereby a torqueKθ being generated around the horizontal shaft of the gyro. This torqueKθ is divided by the angular momentum H of the gyro and is then addedwith a vertical component ω sin λ of the earth rotation angularvelocity, thereby being generated as an angular velocity input. Thisangular velocity input acts on a vertical shaft element 102 of the gyro,and this angular velocity input is added with the initial azimuth errorφ.sub. to produce the azimuth error φ, thereby closing the loop. Thisloop is what might be called a north-seeking loop of the gyro compass.Since two poles expressed by 1/S exist within this loop, this loopbecomes an oscillating solution. On the other hand, a torque μθ isobtained by multiplying the gyro inclined angle θ with the dampingconstant μ and this torque μθ is divided by the angular momentum H so asto provide an angular velocity input. This angular velocity input isnegatively fed back to the horizontal element 101 of the gyro so as todecrease the above inclined angle θ, thereby the north-seeking motion ofthe north-seeking loop being damped. This latter loop is a damping loop.

In order to prevent an acceleration error from being caused in the gyrocompass due to horizontal accelerations, such as increase and decreaseof speed, turning or the like of the ship, the marine gyro compass isgenerally designed such that the north-seeking motion cycle is selectedto be about 90 minutes (Schuler's condition). For this reason, it takesplenty of time for the gyro compass to be settled to the true north soas to be operable since the gyro compass has been energized. This timeis what might be called a settle time.

In the ordinary ships, the above settle time does not raise a problem intheir navigation substantially, however, this long settle time raises aproblem in the ships for some special use.

Accordingly, Japanese Laid-Open Patent Publication No. 1-113611describes a gyro compass having a fast settle apparatus which can reduceits settle time.

This conventional fast settle apparatus will now be described. In such agyro compass which is comprised of a gyro case housing therein a gyrowhose spin axis is kept substantially horizontal, a supporting apparatusfor supporting the gyro case with three-axis freedom and having afunction for outputting an inclined angle of the spin axis of the gyrorelative to the horizontal plane and a function for applying a torque tothe vertical axis of the gyro case in proportion to the input signal,the fast settle apparatus includes a control apparatus which is suppliedwith a signal corresponding to the inclined angle. In this controlapparatus, the signal corresponding to the inclined angle isdifferentiated during a predetermined time since the gyro compass hasbeen energized and a resultant differentiated signal is used as theabove-mentioned input signal, thereby the settle time being reduced.

In the gyro compass having the above fast settle apparatus, if thelatitude at which the gyro compass is located is changed, e.g., at ahigh latitude if the gyro compass is settled by operating the fastsettle apparatus, then the above-mentioned north-seeking motion isplaced in the so-called over-damping state due to the action of thetorque generated around the vertical axis of the gyro by the dampingconstant μ of the damping loop. As a consequence, the settle time isincreased so that, even if the gyro compass is provided with the fastsettle apparatus the settle time cannot be reduced in the high latitudeas expected.

Further, in FIG. 5 which shows a schematic block diagram of the gyrocompass according to the prior art, g represents the gravitationalacceleration, R the earth radius, ω the rotation angular velocity ofearth, H the angular momentum of gyro, λ the latitude at that spot,τ.sub. the time constant provided when the movement of the liquidsurface of the ballistic 6 is approximated by the primary delay, K thenorth-seeking constant, μ the damping constant, α_(N) the accelerationacting on the north-south direction of the gyro case due to the ship'smovement, V_(NS) the north-south velocity of the ship and S the Laplaceoperator.

A sum of the gyro inclined angle θ and a value α_(N) /g, which resultsfrom dividing the north-south acceleration α_(N) by the gravitationalacceleration g, acts on the primary delay transfer element 50 (timeconstant τ₁₀ ) provided by the liquid 6-2 of the ballistic 6 to form theliquid surface inclination ξ.

A precessional angular velocity ##EQU3## provided by multiplying ξ witha value K/H (51), which results from dividing the north-seeking constantK by the angular momentum H of the gyro and which is generated aroundthe vertical axis acts around the vertical axis of the gyro case 52together with the vertical component ω sin λ of the earth rotationangular velocity ω to produce the azimuthal movement around the verticalaxis. Then, the azimuth error φ is generated. A value, which resultsfrom multiplying the azimuthal error φ with the horizontal component ωcos λ 53 of the earth rotation angular velocity ω, is input to a gyroelement 54 around the horizontal axis of the gyro as the angularvelocity input to thereby generate the gyro inclined angle θ.

The above-mentioned portion is what might be called a north-seeking loopof the gyro compass, in which two poles expressed by 1/S exist withinthe loop, thereby generating the oscillation solution.

An angular velocity ##EQU4## which results from dividing by the gyroangular momentum H the torque ##EQU5## around the vertical axis in which##EQU6## which results adding the gyro inclined angle θ with ##EQU7## ismultiplied with the damping constant μ is input to a gyro element 54around the horizontal axis together with the equivalent angular velocityV_(NS) /R which results from dividing the north-south speed V_(NS) ofship by the earth radius R, whereby the gyro inclined angle θ is reducedand the north-seeking movement is damped. Therefore, this loop is calleda damping loop.

For the north-seeking loop, the north-south velocity V_(NS) generates anazimuth error φ_(V) proportional to second of the latitude expressed bythe following equation. ##EQU8## where C is the azimuth angle of theship's heading.

FIG. 6 is a graph illustrating the movement of the gyro when the shipturns by 180° at time t₁ from the condition that the ship sails straightahead on the course 0° for a long time and the gyro compass is settledwith velocity error φ_(V1) at that time and then the ship sails straightahead on the course 180° from time t₂. This fundamental influence of thegyro compass exerted by the acceleration can be reduced to the ordinarygyro compass.

An azimuth change φ_(B) generated by the acceleration between the timet₁ and the time t₂ is called as ballistic amount. A design method formaking the azimuth change φ_(B) equal to the difference between thevelocity errors before and after the acceleration acts is the importantcondition called the Schuler tuning in the gyro compass and corrects theinfluence of the acceleration in the form of velocity error (thenorth-seeking cycle of the gyro compass is extended to 1 to 1.5 hoursdue to this condition). That is,

    φ.sub.B -φ.sub.V1 -φV.sub.2

The above-mentioned ballistic amount φ_(B) is the function of thevelocity difference and the difference of the velocity error is also thefunction of the latitude as expressed in the above-mentioned equation.Therefore, strictly speaking, the condition in the above-mentionedequation is established only in particular latitude (referred to as areference latitude). In other latitudes, the error Δφ of FIG. 6 isgenerated immediately after the ship turns and then in accordance withthe fundamental movement characteristics of the gyro compass, the gyrocompass carries out the damping movement toward the velocity errorφ_(V2) provided immediately after the ship turns.

Instead of the above-mentioned damping weight 7, there is proposed amethod in which the north-seeking movement of the gyro compass iscarried out by, for example, the inclinometer or tilt meter foroutputting the inclined angle of the spin axis of the gyro compassrelative to the horizontal plane, an amplifier supplied with the outputof the tilt meter, a torquer supplied with the output of the ampliferand so on. This method has the advantage such that the dampingcharacteristic of the north-seeking movement can be arbitrarilycorrected only by adjusting the gain of the amplifier.

The system utilizing the electrical torquer instead of the mechanicaldamping weight in order to obtain the above-mentioned damping effectconsiderably depends on accuracy of apparatus for detecting theabove-mentioned reference inclined angle.

However, high efficiency and high accuracy requested for the inclinedangle detecting apparatus of the gyro compass for multipurpose except apart of war-use makes the gyro compass expensive.

As a result, in the gyro compass utilizing the inexpensive inclinedangle detecting apparatus available on the market, an error occurs inthe azimuth transmission angle of the gyro compass due to the errorappearing in the inclined angle detecting apparatus.

OBJECTS AND SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide animproved fast settle apparatus for use with a gyro compass in which theaforementioned shortcomings and disadvantages of the prior art can beeliminated.

More specifically, it is an object of the present invention to provide afast settle apparatus for use with a gyro compass in which fast settletime can be reduced.

It is another object of the present invention to provide an errorcorrecting apparatus for use with a gyro compass in which gyro compasserror can be corrected with ease.

As a first aspect of the present invention, a gyro compass having a gyrocase housing therein a gyro whose spin axis is held substantially in thehorizontal plane, a supporting device for supporting the gyro case withfreedom of three axes, a function for outputting a signal correspondingto an inclined angle of the gyro spin axis relative to the horizontalplane and a function for applying a torque around a vertical axis of thegyro case in proportion to an input signal is comprised of a controlapparatus supplied with the signal corresponding to the inclined angleand a latitude value at which the gyro compass is located, wherein aconstant (or a damping constant) relative to the input latitude value isset by the control apparatus after the gyro compass is energized, asignal, which results from differentiating the signal corresponding tothe inclined angle during a predetermined time, is added to a signal,which results from multiplying the signal corresponding to the inclinedangle with the constant and an added result is set as the input signal,whereby a constant optimum north-seeking movement is carried outregardless of the change of the latitude value to thereby reduce asettle time.

In accordance with a second aspect of tho present invention, a gyrocompass having a gyro case housing therein a gyro whose spin axis isheld substantially in the horizontal plane, a supporting device forsupporting the gyro case with freedom of three axes, a function foroutputting a signal corresponding to an inclined angle of the gyro spinaxis relative to the horizontal plane, a function for applying a torquearound a vertical axis of the gyro case in proportion to an input signaland an azimuth transmitter for transmitting an azimuth of the spin axisrelative to a navigation vehicle is comprised of an error correctingapparatus supplied with the signal corresponding to the inclined angle,a speed signal of the navigation vehicle and a ship's heading azimuthsignal thereof, wherein a bias error caused by the inclined angle of thegyro compass spin axis relative to the horizontal plane and an azimutherror caused by the movement of the navigation vehicle are estimated andcalculated to thereby reduce an azimuth error caused by the bias error.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following detailed descriptionof illustrative embodiments thereof to be read in conjuction with theaccompanying drawings, in which like reference numerals are used toidentify the same or similar parts in the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a conventional gyro compass in a perspectiveview fashion and to which the present invention is applied;

FIG. 2 shows a schematic diagram of a liquid ballistic used in theconventional gyro compass of FIG. 1;

FIG. 3 is a schematic diagram used to explain a principle of the dampingweight used in the prior-art gyro compass shown in FIG. 1;

FIG. 4 is a schematic block diagram used to explain a principle of theconventional gyro compass shown in FIG. 1;

FIG. 5 shows a functional block diagram of the gyro compass shown inFIG. 1;

FIG. 6 is a graph to which references will be made in explaining a gyrocompass error caused when a navigation vehicle is moved;

FIG. 7 shows a perspective view of a gyro compass to which a fast settleapparatus of a first embodiment according to the present invention isapplied;

FIG. 8 shows a schematic block diagram used to explain a principle ofthe present invention;

FIG. 9 shows in block form a gyro compass to which an error correctingapparatus according to the present invention is applied; and

FIG. 10, which is formed of FIGS. 10A and 10B drawn on two sheets ofdrawings so as to permit the use of a suitably large scale, is a blockdiagram showing an embodiment of the error correcting apparatus of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of a fast settle apparatus for use with the gyrocompass A according to the present invention will now be described withreference to FIG. 7. In this embodiment, the fast settle apparatus alsois applied to the foregoing gyro compass shown in FIG. 1. Accordingly,in FIG. 7, like parts corresponding to those of FIG. 1 are marked withthe same references and therefore need no be described in detail.

The first embodiment of the present invention shown in FIG. 7 isdifferent from the aforementioned example of the prior art shown in FIG.1 only in the following points:

In the first embodiment of the present invention shown in FIG. 7, thevertical ring 3 has mounted thereon a tilt meter 50, the input axis ofwhich is in parallel with the spin axis of the gyro rotor;

the vertical ring 3 and the gyro case 1 have mounted therebetween avertical torquer which applies a torque proportional to an input currentto the vertical shafts 2, 2' of the gyro case 1; and

a control apparatus 52 is provided to receive an output signal 50A(proportional to an inclined angle of the gyro spin axis relative to thehorizon) and a latitude value set by the external unit and to supply anoutput signal 51A to the vertical torquer 51, thereby removing thedamping weight 7.

Referring to FIG. 7, it will be seen that the control apparatus 52 iscomprised of a timer apparatus 62, a switch 61 controlled by the timerapparatus 62, a control amplifier 60 for generating a damping signal foreffecting the fast settle, and a constant setting unit 63 for setting adamping constant. The switch 61 is turned on and off by the modechange-over signal from the timer apparatus 62 so that the output signal51A is controlled. The timer apparatus 62 is energized by a switch-onsignal SWA of the gyro compass or by a signal equivalent to theswitch-on signal SWA and generates a signal for turning off the switch61 after a predetermined fast-settle time is passed. A period during thetimer apparatus 62 is operated is called a fast-settle mode (a periodafter this fast-settle mode is called a navigation mode).

A control apparatus 52 of the present invention will be described withreference to FIG. 8.

In the control apparatus 52, during the fast settle mode, a constantrelative to the initial input latitude value λ is set by the constantsetting device 63. This constant is equivalent to a constant of theconventional damping weight and will hereinafter be determined as adamping constant μ'. By the action of the damping constant λ', amechanical damping action of the north-damping seeking movement done bythe conventional damping weight is effected electrically. The dampingconstant μ' thus determined is set to μ' in the control amplifier 60.

In the above-mentioned constant setting device 63, the damping constantμ' relative to the latitude value λ is expressed by the followingequation: ##EQU9## where μ and cos λ.sub. represent constants by whichthe north-seeking movement is optimized.

From the above-mentioned equation, the damping constant λ' relative tothe latitude value λ is proportional to (cos λ)^(1/2).

The control amplifier 60 will be described next. The output signal 50Aof the tilt meter 50 is input through the control amplifier 60 to thevertical torquer 51 as the control signal 51A. An example of thetransfer function of the control amplifier 60 is expressed by thefollowing equation: ##EQU10## where τ_(f) is the time constant of aswinging filter, η the differentiation time and S the Laplace operator,respectively.

In this example, the control amplifier 60 has a differentiation functionand a multiplication (or proportion) function, and positively feeds thetorque proportional to the differentiated time of the inclined angle ofthe gyro spin axis (i.e., the output signal 50A of the tilt meter 50)back to the vertical torquer 51 by the former function thereof. Morespecifically, when the gyro spin axis (e.g., the north-seeking end) ismoved upwards, then its ascending speed is increased more. Conversely,when the gyro spin axis is moved downwards, then its descending speed isincreased, thereby the cycle of the north-seeking movement beingreduced. Further, the control amplifier 60 performs, by the latterfunction thereof, the electrical damping action instead of themechanical damping action done by the conventional damping weight sothat the optimum constant north-seeking movement is carried out for thechange of the latitude, thus making it possible to reduce the settletime considerably.

The embodiment of the present invention shown in FIG. 8 is differentfrom the example of the prior art shown in FIG. 4 as follows.

That is, the constant setting device 63 for setting the optimum dampingconstant μ' relative to the latitude value λ, the differentiation andthe damping constant μ' are added to the example of FIG. 4 as shown by aone-dot chain line in FIG. 8. In FIG. 8, for simplicity, thetransmission function of the control amplifier 60 is represented by thedifferentiation element S and the damping constant μ', and the gain fromthe tilt meter 50 for detecting the inclined angle θ of the gyro to thevertical torquer 51 is represented by θS-μ'.

Calculating the characteristic equation which expresses the movement ofthe azimuthal error φ of FIG. 8, we have:

    (H-η) φ+μ' φ+Kωcos λ·φ=0

As a consequence, by the addition of the fast-settle mode shown by η,the fast-settle mode η acts to reduce the angular momentum H of thegyro. From the above equation, the north-seeking movement proper cycleTn of the gyro is expressed as: ##EQU11## Also, a half-periodattenuation factor F which expresses the damping degree is expressed as:##EQU12## It is clear from the above-mentioned equation that thehalf-period attenuation factor F is constant relative to the latitude atwhich the gyro compass is disposed. That is, the half-period attenuationfactor F is constant relative to any latitude values.

More specifically, in the fast-settle mode, the gyro cycle Tn can bereduced by the application of torque ηθ around the vertical axis of thegyro and the following equation is established. ##EQU13## If μ.sub.represents a proper damping constant, then it is to be understood thatthe value of the half-period damping factor F can always be madeconstant relative to the latitude value λ. Therefore, if μ.sub. isselected so as to effect the optimum north-seeking operation, then theoptimum half-period attenuation factor F can be obtained, which can as aresult considerably reduce the settle time of the conventional gyrocompass.

Incidentally, as clear from the above-mentioned equation, in order tomaintain the north-seeking movement stable, the following inequalitymust be established:

    η<H

Further, by adding the slew mode in which the follow-up ring 13 isrotated to become coincident with the correct ship's heading by applyinga voltage to the azimuth servo motor 19 before the gyro rotor isenergized, it is possible to reduce the settle time more.

While the present invention is applied to the gyro compass whichincludes neither the tilt meter nor vertical torquer shown in FIG. 1 asdescribed above, the present invention is not limited thereto and may beapplied to a gyro compass having, for example, a tilt meter function,that is, the function in which a signal corresponding to an inclinedangle of the spin axis relative to the horizon and a torque to the inputsignal is applied around the vertical axis of the gyro and the functionin which a damping gain can be corrected by the latitude value. In thiscase, if the gyro compass has the above-mentioned functions, then suchfunctions are utilized, that is, without newly providing the tilt meterand the vertical torquer, the control apparatus of the present inventionis additionally provided, and then it is possible to obtain the gyrocompass in which the optimum north-seeking movement is effectedregardless of the change of the latitude value to thereby reduce thesettle time.

According to the present invention, by adding the fast-settle apparatusof the above configuration, it is possible to obtain the gyro compass ofsimplified arrangement which can be made inexpensive and whose settletime is short regardless of the change of the latitude. Although thesettle time is increased with the increase of the latitude value in theprior art, according to the present invention, the settle time can beprevented from being increased with the increase of the latitude valueso that the settle time can be reduced really. At that time, if thesignal corresponding to the time differentiation of the gyro spin axisis applied as the torque around the vertical axis, then the short settletime can be achieved by the simple calculation. Further, as comparedwith the conventional method in which the north-seeking torque (aroundthe horizontal axis) is increased, according to the present invention(the torque around the vertical axis according to the system of thepresent invention), the torque necessary for the fast settle operationmay be small so that the torquer may be small in size or that theamplifier of small power consumption may be utilized.

While the electric type damping system is described in theabove-mentioned embodiment, the conventional mechanical type dampingsystem can also be applied to the present invention, in which case, adifference of the mechanical damping system relative to the optimumdamping gain may be corrected by the torquer.

An example of an error correcting apparatus which can be applied to thegyro compass of the present invention will be described below withreference to FIGS. 9 and 10.

In FIG. 9, reference symbol A generally designates an example of thegyro compass to which the present invention can be applied. This gyrocompass A is substantially the same as that described earlier withreference to FIGS. 1 to 5. Accordingly, in FIG. 9, like partscorresponding to those of FIGS. 1 to 5 are marked with the samereferences and therefore need not be described.

FIG. 9 shows in block form the gyro compass A which is comprised of anerror correcting apparatus 100, a tilt meter 61 instead of themechanical damping weight having a gain K_(ACC) provided as an apparatusfor outputting an inclined angle of the gyro spin axis relative to thehorizon instead of the mechanical damping weight, an amplifier 62 havinga gain μ' which is supplied with the output of the tilt meter 61 and atorquer 63 having a gain K_(T) around the vertical axis which issupplied with the output of the amplifier 62.

A relation between the damping constant μ and the gain μ' of FIG. 5 isexpressed by the following equation (1)

    μ=K.sub.ACC ·μ'·K.sub.T            (1)

The gyro compass A to which the gyro compass error correcting apparatus100 of the present invention is applied will be described below.

For simplicity, the azimuthal error φ produced at the timing point aftersufficient settle time is expressed by the following equation from FIG.1: ##EQU14## where μ is the damping constant which can be described bythe relation of the equation (1), ω the rotational angular velocity ofthe earth, λ the latitude of the position at which the gyro compass islocated, K the north-seeking gain, ME the error angle at which aninclined angle detecting apparatus is attached to the horizon of thespin axis, AB the term expressed by the sum of drift items changed by afixed bias proper to the inclined angle detecting apparatus, atemperature or the like, T.sub.θ the mechanical umbalance torque amountaround the horizontal axis, V_(NS) the velocity of navigation vehicle inthe north-to-south axis direction with its north direction as +, and Rthe radius of the earth.

Accordingly, the azimuthal error φ is expressed by errors generatedaround four axes parallel to the spin axis.

As described above, due to the fixed bias of the tilt meter 61 which isthe inclined angle detecting apparatus for the gyro spin axis, the termAB expressed by the sum of drifts changed with the temperature or thelike and the north-south axis velocity of the navigation vehicle, theazimuthal error of the gyro compass A takes place.

As shown in FIG. 9, the error correcting apparatus 100 of the presentinvention is supplied with the inclined angle signal from the gyrocompass, that is, a detected inclined signal SA derived from the tiltmeter 61, an azimuth signal A_(z), a velocity signal V' of thenavigation vehicle having the gyro compass or the like. The errorcorrecting apparatus 100 derives a correcting signal Al for correcting abias error caused by the inclined angle signal of the gyro compass andan actual azimuth signal Azt from which an error caused by the movementof the navigation vehicle is removed.

FIG. 10 shows more in detail the arrangement of the error correctingapparatus 100. In this case, FIG. 10 is formed of FIGS. 10A and 10Bdrawn on two sheets of drawings so as to permit the use of a suitablylarge scale.

Referring to FIG. 10, the error correcting apparatus 100 is composed ofan error calculating unit 100A, a bias error correcting unit 100B and anazimuth error correcting unit 100C. The error calculating unit 100Afurther includes a model calculating unit 100A1, an error detecting unit100A2 for the model calculating unit 100A1 and an external informationprocessing unit 100A3.

The above-mentioned respective units will be described with reference toFIG. 10. The model calculating unit 100A1 of the error calculating unit100A is designed so as to have the same characteristic as that of thegyro compass shown in FIG. 9 and therefore both of them includesubstantially the same elements 50 to 54A.

In the error detecting unit 100A2 for the model calculating unit 100A1in the error calculating unit 100A, it is determined by comparing thegyro compass detection inclined signal SA with the equivalent inclinedsignal SB from the model calculating unit 100A1 by a comparator 101whether or not the model calculating unit 100Al is coincident with thegyro compass. If they are not coincident with each other, a differencetherebetween is multiplied with gains Kθ, Kφ and Kb by coefficientgenerators 102, 103 and 104 to thereby supply first, second and thirdcorrecting amounts εθ, εφ and εb to the model calculating unit 100A1, inwhich values θ, φ and b of the model calculating unit 100A1 arecorrected one more time.

In the external information processing unit 100A3 of the errorcalculating unit 100A, values V'ns and V'ns necessary for presenting thesame situation as the situation in which the gyro compass is affected bythe movement of the navigation vehicle are calculated by the north-southvelocity calculating unit 105 and the differentiator 106.

Accordingly, the above-mentioned error calculating unit 100A includesthe error detecting unit 100A2 for the model calculating unit 100Alwhich acts as a negative feedback loop in such a fashion that theequivalent inclined signal SB from the model calculating unit 100A1becomes coincident with the detection inclined signal SA from the gyrocompass.

The gains Kθ, Kφ and Kb in the error detecting unit 100A2 for the modelcalculating unit 100Al need not be described herein because they areobtained by Kalman filter theory or observer theory in the controlengineering or by the method of least square in the statistics and soon.

The bias error correcting unit 100B receives an equivalent biasestimator, which will be described later, from the abovementioned errorcalculating unit 100A and feed the correcting signals A1, A2 through thecoefficient generators 107, 108 having correcting gains K_(FB1), K_(FB2)back to the gyro compass and the model calculating unit 100Al, therebycorrecting the azimuthal error caused by the equivalent bias amount.

The above-mentioned correcting gains are expressed by the followingequations: ##EQU15##

The azimuth error correcting unit 100C generates a true azimuth signalAzt by such a manner that an azimuth error estimated amount, which willbe described later, is derived from the above-mentioned errorcalculating unit 100A and then subtracted from the azimuth signal Az tothereby remove the azimuthal error involved in the azimuth signal Az.

Specific operation of the error calculating unit 100A will be describedbelow.

Initially, the detection inclined signal SA from the gyro compass isdivided by K_(ACC) by the coefficient generator 109 of the errordetecting unit 100A2 for the model calculating unit 100A1 because theunit system must be made coincident with the equivalent inclined signalSB from the model calculating unit 100A1. The signal thus divided andthe equivalent inclined signal SB from the model calculating unit 100A1are input through the comparator 101 in the error detecting unit 100A2for the model calculating unit 100A1 to the coefficient generators 102,103, 104 having the gains Kθ, Kφ and Kb.

In the error detecting unit 100A2 for the model calculating unit 100A1the value, which results from subtracting the equivalent inclined signalSB from the model calculating unit 100A1 from the gyro compass detectioninclined signal SA, is multiplied with the gains Kθ, Kφ and Kb tothereby generate values εθ, εφ and εb, respectively.

In the model calculating unit 100A1 the value εθ is the correctingamount of the estimated value θ of the inclined signal in the modelcalculating unit 100A1, εφ the correcting amount of the estimated valueφ of the azimuthal error and εb the correcting amount of the estimatedvalue b of the equivalent bias, respectively.

By these correcting amounts εθ, εφ and εb, the respective estimatedamounts of the model calculating unit 100A1 are corrected and the gyrocompass detection inclined signal SA and the equivalent inclined signalSB estimated amount from the model calculating unit 100Al are againcompared with each other by the error detecting unit 100A2 for the modelcalculating unit 100A1. This comparison is continued until the inclinedsignal estimated value becomes coincident with the inclined signal. Atthat time, in order to supply the model calculating unit 100Al with theinfluence substantially equal to those of the north-south axis directionvelocity Vns and the north-south axis acceleration V'ns acting on thegyro compass when the navigation vehicle is moved, the signals V'ns andV'ns from the external information processing unit 100A3 which issupplied with the velocity signal V' and the azimuth signal Az arecaused to act on the model calculating unit 100A1.

As a consequence, in the error calculating unit 100A, the inclinedsignal estimated value θ becomes coincident with the inclined signal θof the gyro compass.

Therefore, the inclined signal error estimated value φ within the modelcalculating unit 100A1 coincides with the azimuth error of the gyrocompass and the estimated value of the bias value becomes equal to thebias value which generates the inclined signal θ of the gyro compass.

By the provision of the error correcting apparatus to receive thedetection inclined signal SA of the gyro compass and to output thecorrecting signal Al to the torquer around the vertical axis in whichthe inclined angle of the spin axis of the gyro compass relative to thehorizontal plane is calculated as the equivalent bias value b, the errorof the tilt meter caused by the fixed bias component included in theapparatus such as a tilt meter and by the drift component changing withthe change of temperature or the like, the mount error of theinclination detecting apparatus relative to the horizontal plane of thegyro compass spin axis, the horizontal axis torque error caused by themechanical unbalance state around the gyro compass spin axis (ornorth-south axis), the latitude error caused by the earth rotationcomponent input to the gyro compass with the change of the latitude andso on are treated as the bias component acting on the gyro compass, thiscomponent can be calculated and corrected with ease.

Therefore, according to the error correcting apparatus of the presentinvention, this equivalent bias value b is calculated and the torquer ofthe gyro compass is corrected, thus making it possible to eliminate theazimuthal error caused by the inclined angle θ.

Further, by adding the error correcting apparatus of the presentinvention to the gyro compass without changing the conventionalcharacteristics, it is possible to reduce the error considerably.

Furthermore, according to the error correcting apparatus of the presentinvention, in the damping operation done by the inclined angle θ of thegyro compass, the signal effects to separate the north-seeking movementof the gyro compass and the signal for causing the azimuthal error fromeach other and only the signal for causing the azimuthal error isremoved to thereby extract the azimuthal error caused by the biascomponent. Also, the error caused by the acceleration accompanying withthe movement of the navigation vehicle can be removed from the azimuthsignal. In addition, φ can be estimated during a short period of time byadjusting the gains Kθ, Kφ and Kb in the error detecting unit of themodel calculating unit 100A1. Thus, the error correcting apparatus ofthe present invention can be utilized as the fast-settle apparatus.

Having described the preferred embodiments of the invention withreference to the accompanying drawings, it is to be understood that theinvention is not limited to those precise embodiments and that variouschanges and modifications thereof could be effected by one skilled inthe art without departing from the spirit or scope of the novel conceptsof the invention as defined in the appended claims.

What is claimed is:
 1. A gyro compass comprising a casing supported formovement freely in three axes; a gyro located in said casing having itsspin axis arranged to normally lie in a substantially horizontal axis;means for producing a signal corresponding to the angle of inclinationof the spin axis; means for applying a torque around the vertical one ofsaid axis to modify the movement of said casing and control apparatuscomprising an input for receiving the signal indicative of the angle ofinclination of said spin axis, an input for receiving a signalindicative of the latitude at which said compass is located, means forgenerating a constant relative to said latitude after said compass isenergized, means for differentiating the signal indicative of the angleof inclination of said spin axis during a predetermined time andproducing a signal corresponding thereto, means for mutliplying saidsignal corresponding to the angle of inclination of said spin axis withsaid constant and corresponding a signal corresponding thereto, meansfor adding said differentiation signal and said multiplication signaland producing an addition signal, means for applying said additionsignal to said means for modifying the movement of said casing whereby aconstant optimum north-seeking movement is obtained regardless of anychange of latitude so as to reduce the settle time of said compass.